Method and apparatus for casting concrete bodies with cavities therein



2 SHEETSSHEET 1 M. VAN BUREN METHOD AND APPARATUS FOR CASTING CONCRETEBODIES WITH CAVIT IES THEREIN July 15, 1952 Filed Dec. 8. 1949 INVENTOR.MYERS VAN Bureau.

40144, A? s 'nu/ AT OKNEKS.

Filed D30. 8, 1949 2, SHEETS-SHEET 2 I 41 m I i 8 2 .7

m 37 1Q I '22 INVENTOR.

MYEI RSVAN Bureau. 2 BY y 15, 1952 M. VAN BUREN 2,602,979 METHOD ANDAPPARATUS FOR CASTING CONCRETE BQDIES WITH CAVITIES THEREIN 30ATTOKA/EVJ Patented July 15, 1952 METHOD AND APPARATUS FOR CASTINGCONCRETE BODIES WITH CAVITIES THEREIN Myers Van Buren, Haworth, N. 3.,assignor to Raymond Concrete Pile Company, New York, N. Y., acorporation of New Jersey Application December 8, 1949, Serial No.131,816

6 Claims.

This invention relates to methods and apparatus for molding concrete andthe like by spinning operations, the invention being particularlyadapted, among other possibilities, for the manufacture of tubularconcrete sections having in the walls thereof circumferentially spacedcavities extending longitudinally of the axis of the tubular member.

Tubular concrete sections or members of the type indicated are welladapted for use in endto-end relation for forming continuous lengths ofconcrete pipe and certain types of piles or tubular columns, with theabove-mentioned cavities in succeeding sections positioned in alignmentwhereby wires or other reinforcing means may be threaded therethroughand subjected to heavy tension for longitudinally restressing theassembly of tubular sections and to hold same tightly togetherend-to-end with sealing means therebetween if desired, under heavypressure. There are well known advantages in the method of formingtubular concrete members by spinning a mass of concrete in a rotatablemolding apparatus, but the forming of longitudinal cavities in the wallsof such members accurately, uniformly and economically in connectionwith such spinning operations involves difllculties which, so far as isknown have not heretofore been satisfactorily overcome.

If such cavities are to be used to contain reinforcements under heavytension for prestressing purposes, it is important that they beaccurately formed and positioned, and free of any curvatures againstwhich the prestressing cables or the like might bear and causeunpredictable transverse stresses in the completed assembly of sectionswhen in use. Yet if a simple form of mandrel is usedin the rapidlyrotating molding apparatus to .definesuch a cavity, the centrifugalforce acting on the unsupported portions of such a mandrel will tend'tocauseit to deflect objectionably, thereby producing a somewhat curvedcavity. Further problems arise in providing suitable supportingstructure for the mandrels Various further and more specific objects,

features and'advantages of the invention will appear from thedescription given below taken in connection with the accompanyingdrawing forming a part of this specification and illustrating by way ofexample a preferred embodiment of the invention.

In the drawings: Y I Fig. 1 is a horizontal sectional view of apreferred form of apparatus for carrying out'the invention and involvingthe .novelfeatures thereof and showing the parts of the apparatus in thepositions which they occupy during the operation oi molding a tubularconcrete member with thereof such as above recross-sectional shape ofthe concrete member to.

be molded therein. The drum I0 is preferably formed of an area of sheetmetal, so shaped that two longitudinaledges thereof are brought to,-gether' and removably held in place as by bolts I l which pass throughtwo angle bars as at l2 welded or otherwise secured respectively tosuchlongitudinal'edges in a manner which will be readily understood fromFig. 1. Two annular tracks as at 13 are provided around the exterior ofthis drum and are adapted to roll on rollers as indicated at [6 topermit spinning of the drum (by a suitable source of power, not shown)about its longitudinal axis, witha mass of concrete therein, and so thatthe centrifugal force of the spinning will cause the concrete todistribute itself over the inside surfaces of the drum to form tubularconcrete member as at [1. v I

Removable end pieces or barrier members as at H3 or I9 of likeconstruction are provided at each end of the drum, the inner surfaces ofthese members as at 20, 2| servingto define the end surfaces of theconcrete memb'erll being molded. Each of these barrier memberspreferably comprises a cylindrical or annular web portion as at 22 whichis cast integral with or is welded to annular flange portionsas at23,24, said surfaces 20, 2| being formed on the flange portions as at23, which are also preferably so shaped as to protrude slightly into theendof the sheet metal 3 drum to an extent limited by the small annularlip portions as at 23.

A plurality of removable mandrel means as at 25 are provided, the samebeing of the shape and position of the desired cavities to be formed inthe concrete body ll, viz. in the particular example shown such cavitiesare to be cylindrical in form, to extend longitudinally of the concretemember I! at circumferentially spaced positions around within the wallsof the member.

As shown in Fig. 2, each of such mandrel means preferably comprises aninner rigid core member- 26 preferably of metal, surrounded by a sheathof readily stretchable rubber as at 21. Natural rubber may be used forthis purpose, or if preferred, various suitable well-known types ofsynthetic rubber or rubber-like stretchable materials are available forthe purpose.

The core 26 will usually be hollowed out, that is, in the form of ametal tube, although in some cases, particularly if a light metal isused, the core may comprise a solid rod. But in any event, the mandrelmeans is preferably so designed as to have an over-all specific gravitythe same as, or approximating the specific gravity of the concrete asmolded to form'the member H. The expression over-all specific gravity asused herein and in the appended claims, has reference to the specificgravity which each. complete crosssectional portion of the mandrel meanswill have, taking into account the specific gravities of the sheath andcore materials and the space within the core, if any (ordinarily filledwith air). It will be apparent that such over-all specific gravityapproximating that of the concrete may be readily obtained by properselection of the materials used and their relative dimensions, takinginto account the specific gravity of each of the two materials andconsidering the space, if any, provided within the core.

The purpose and advantage of designing the mandrel means in this way isto obviate the deflections or distortions which would otherwise occur inthe. mandrel. means under the powerful centrifugal force to which it issubjected durin spinning of the apparatus. That is, since the mandrelmeans is supported rigidly at its respective ends by means such ashereinafter described, and it will be apparent that the metal portionsparticularly of each mandrel necessarily have considerable weight, thelatter will, upon being subjected to centrifugal force during thespinning operation, be deflected outwardly in the event the concretemixture is lighter than the mandrel means, or inwardly in the event theconcrete mixture is heavier. Since during the setting of the concrete,the drum will ordinarily be subjected to a spinning, motion with aci-rcumferential speed for example as high as 3000 feet per minute, itwill be apparent that such deflections will be substantial, if there isa substantial difference between the specific gravities of the concreteand the mandrel means. The cavities being formed in the. concrete wouldthen be curved or distorted in shape, giving rise to the objectionsabove explained.

Commonly used concrete mixtures have a specific gravity in theneighborhood of 2.4. Hence, with such mixtures the mandrel means shouldvbe so designed as to have substantially the same over-all specificgravity. However, it will bev appreciated that the specific gravity ofconcrete may vary considerably depending upon the characteristics ofstrength, weight, etc. desired in the finished structure, but usually ifthe mandrel means is designed to have a specific gravity somewherebetween about 2 and 2.8, this will satisfy the requirements for use withconcretes of different weights within the ordinarily practical range,and still enable the mandrel means to be adequately supported andretained by the concrete against prohibitive deflections. In case themixture has an unusually low specific gravity, as in the case of certainfoam-like mixtures for example, then the mandrel means should bedesigned to have an equally low specific gravity.

As hereinafter explained, the mandrel cores, while in use, arepreferably placed under substantial longitudinal tension which will beeffective in further preventing deflections of the mandrels in the eventtheir over-all specific gravity differs within reasonable limits fromthat of the concrete.

Since both end portions of the mandrels will ordinarily be rigidlysupported, it is of course not important that such end portions, asdistinguished from the middle portions, be designed to have a particularspecific gravity, Yet for simplicity, and as shown in Fig. 2, it willordinarily be convenient to form both the core and the rubber sheathportions with uniform crosssectional dimensions substantially throughouttheir lengths.

The supporting and tensioning means for the ends of the mandrels willnow be described with reference to Fig. 2. One end of each mandrel coremember, as shown, is provided with a threaded plug 21 adapted to receivea nut as at 28 to bear against a washer 29, which in turn bears againsta flange portion on an end piece 18 or l9. The other end of the mandrelcore is formed with a transverse slot or slots 30 through which keymeans as at 3i (Fig. 1) are adapted to be inserted to retain such endagainst movement when the nuts as at 28 are tightened to the extentdesired for tensioning the mandrels and also to retain the end pieces orbarrier members i8 and i9 tightly in position against the ends of thedrum ill.

The end of the. mandrel core which has the threaded plug 21 is. alsopreferably formed with an external threaded portion 3|, which isembraced by the corresponding end of the rubber sheath, the latter beingsecurely retained on the threaded portion 3| as by tightly wrapping samewith a helix of wire as at 32, sothat the rubber is depressed into thethreads at 3| and held against longitudinal displacement with respectthereto.

The flange portions 23, 24 are formed with aligned apertures. forreceiving the end portions of the mandrels. To prevent escape of theconcrete mixture or water therefrom along the mandrels through theapertures in the flanges 23, such apertures are provided with stuflingbox means as at 33, 33. These may be formed by providing an annularcollar as at 34 welded to the fiangeportion 23 and adapted to receive agasket shaped with, a cross-section as indicated at 35 and held in placeby a thimble member 36. The latter member extends up into engagementwith the washer 29 so that when the nut 28 is tightened, the lower endof the thimble member is crowded down against the gasket and the latteris forced into firm engagement around its periphery with the collar 34and into tightly fitting embracing relation with the rubber sheath 21.

If the tubular concrete members I! are to be used in prestressedend-to-end relationship as hereinabove explained, it will be desirableto provide an enlargement as at 35 at each end of each longitudinalcavity formed by' the mandrel means, such enlargement providing spacefor grout to seal the prestressing wires atthe abutting ends of theconcrete 'sections'f Such enlargements may be formed by'providing asuitably shaped thimble-lik'e member as at 31 fitted into the aperturein the flange portion 23 and having a portion adapted to protrude intothe mass of concrete to the extent indicated at 36. Also it is desirablethat the concrete member I! be so formed that the outer peripheral edgesof the end surfaces will be rounded." To accomplish this, the flangeportions 23 may be as at 39. r

In using the apparatus, the mandrel parts are first designed or selectedso as to provide approximately the, proper specific gravity as aboveexplained, and these are inserted in the end pieces and assembled in themanner indicated in Fig. l, the nuts 28 being tightened with the keys 3|in place whereby the mandrel cores will be longitudinally tensioned andthe drum end pieces will be securely held in place. Then with the drumin horizontal position resting on the rollers 16, it is rotated by powerdriven means at a rate such that its peripheral speed will be severalhundred feet per minute. During this time, a mass of the concrete isintroduced through either or both ends of the drum structure, and aftersufficient concrete is introduced, the spinning speed is increased andmaintained for example at about 3000 feet per minute, until the concretehas become set to a degree permitting its removal from the apparatus.Usually some reinforcing means will also be provided in the concrete tofacilitate its handling at this stage without breakage. For example, asindicated in Fig. 1, a length of wire may be provided for this purpose,shaped in the form of a helix, the cross-sections of its turns beingindicated at 40, and same being located in positions to surround all ofthe mandrel means.

In order to remove the mandrel means, the drum structure is preferablymoved to a vertical position and then the nuts 28 are loosened and thekeys 3| are removed. Thereupon derrick means may be connected to thelifting eyelet members 4| on the end piece l9, whereupon this member isslowly lifted along with all of the several mandrel means as a unitaryassembly. While the rubber sheathswill tend to remain adhered to theconcrete, they will stretch first at the upper portions and thenprogressively further down as at 42, with the result that the successiveportions of the rubber will readily become released from the concrete inthe cavities as the cores are elevated. That is, the rubber will bereleased not only because of the upward pulling and stretching, but alsobecause of the consequent reduction in diameter of the sheaths. Theexterior surfaces of the core members may be lubricated if necessary tofacilitate easy sliding thereof upwardly within such portions of thesheaths as have not been stretched and released at any stage of theoperation of withdrawing the mandrels. It will be noted that theloosening of the nuts 28 will serve to release the pressure of thestufling boxes against the rubber sheaths so that the stuffing boxeswill not interfere with the upward stretching and withdrawal of thesheaths.

After the mandrels and end pieces of the assembly are removed, theconcrete body I! may be readily removed upon loosening the bolts llformed with inwardlyextending annular ridges v6 along the side of thedrum-to permit the drum to expand to partially open condition.

After the concrete'body has been removed, it will be apparent that allof the partsmay be re-assembled and re-used in the'mannershown inFig. 1.v I P Although certain particularembodiments of the invention are hereindisclosed-for purposes of explanation, various further modificationsthereof, after study of this specification, will be apparent to thoseskilled in the art to which the invention pertains. Reference shouldaccordingly be had to the appended claims in determining the scope ofthe'inv'ention.

What is claimed and desired to be secured .by Letters Patent is: T

1. In apparatus for molding tubular concrete members having"longitudinal cavities at circumferentially spaced positions within thewalls, the combination comprising a rotatable tubular chamber, removablebarrier means 'at the ends of said chamber for "defining the ends of theconcrete members, a plurality of mandrels each passing through saidchamber and through apertures in said barrier means and having the shapeand positions of the desired cavities, sealing gaskets embracing themandrels at'said apertures, releasable means atthe mandrel ends forlongitudinally tensioning same, Land; elements interposed between thelatter means' andgsaid gaskets to apply pressure fromisuch tensioningmeans to said gasketswhe n, theimandrels are tensioned. y f

2. In combination with 'rotatable molding apparatus adapted for theformation therein of tubular concrete members by spinning,longitudinally removable mandrel means supported adjacent its ends inthe apparatus in a position to extend generally longitudinally withinthe wall of the concrete member being formed, to form a cavity therein,said mandrel means comprising a relatively rigid core surrounded by areadily stretchable covering, releasable threaded means at an end ofsaid core for tensioning same during use in the apparatus, and stufiingbox means embracing said covering and against which such tensioningmeans exerts pressure when in use, to tighten said stufiing box means.

3. In apparatus for molding tubular concrete members having longitudinalcavities at circumferentially spaced positions within the Walls thereof,the combination comprising a rotatable tubular chamber, barrier means atan end of said chamber, a plurality of mandrels each passing throughsaid chamber and having the shape and positions of the desired cavities,said barrier means including two interconnected flanges with alignedapertures through which the mandrels pass, the first of said flangesdefining an end of the chamber space, the second of said flanges beingspaced outwardly of the chamber from the first, gasket means embracingthe mandrels at said first flange and means at the second of saidflanges for longitudinally tensioning the mandrels, and elementsinterposed between said tensioning means and said gaskets for applyingsealing pressure to the gaskets from such tensioning means.

4. In the molding of concrete in a rapidly r-otating chamber havingmandrel means supported therein in an off-center relation to the axis ofrotation to form a cavity in the concrete, the method of avoidingsubstantial deflection of such mandrel means due to the action of thecentrifugal force of the rotation, which method com- 7. prisesintroducing into the chamber a mass of a concrete mixture havingapproximately the same specific gravity as the overall specific gravityof at least that portion of the mandrel means used which is spaced fromits points of support, and rapidly rotating the chamber withsuchconcrete mixture therein until the mixture has set, the amount ofsuch mixture introduced being sufiicient, when distributed around in thechamber by centrifugal force, to cover the mandrelmeans.

5. In the molding of concrete in a rotating chamber having mandrel meanssupported therein at the end walls of the chamber and extending along inspaced relation to the axis of rotation to form a cavity in theconcrete,the method of avoiding substantial deflection of such mandrel means dueto the action of the centrifugal force of the rotation, which methodcomprises introducing into the chamber a mass of a concrete mixturehaving aproximately the same specific gravity as the overall specificgravity of at least that portion of the mandrel means used which isspaced from its points of support, and, while maintaining the mandrelmeans under a substantial longitudinal tensioning force reactinginwardly on the end walls of the chamber, rapidly rotating the chamberwith such concrete mixture therein until the mixture has set, the amountof such mixture introduced being suificient, when distributed around inthe chamber by centrifugal force, to cover the mandrel means.

6. In the molding of concrete in a rapidly rotating chamber havingmandrel means comprising a relatively rigid core covered by a readilystretchable sheath supported in, the chamber 8, and extending along thedirection of, but in spaced relation tothe axis of rotation to form acavity in the concrete, the method of avoiding substantial deflection ofsuch mandrel means due to gravity and the action of the centrifugalforce of the rotation, which method comprises introducing into thechamber a mass of a concrete mixture having. approximately the samespecific gravity as the overall specific gravity of at least thatportion of the mandrel means used which is spaced from its points ofsupport, and, while maintaining the core of the mandrel means undersubstantial longitudinal tension, rapidly rotating the chamber with suchconcrete mixture therein until the mixture has set, the amount ofsuchmixture introduced being suflicient to cover the mandrel means duringsuch rotation.

MYERS VAN BUREN.

REFERENCES oi'rEn l'he following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,365,753 Vought Jan. 18, 19211,408,685 Benson Mar. 7, 1922 1,955,760 Nichols Apr. 24, 1934 2,052,126Brush Aug. 25, 1936 2,236,616 Bosco Apr. 1, 1941 FOREIGN PATENTS NumberCountry Date 434,538 Great Britain Sept. 4, 1935

